1. Field
The presently disclosed subject matter relates to semiconductor light-emitting devices in which light emitted from a semiconductor light-emitting chip is wavelength-converted by a wavelength-converting layer, and to manufacturing methods for the same. More particularly, the disclosed subject matter relates to semiconductor light-emitting devices for a vehicle light and the like, which can emit a mixture light having a high uniformity from a small light-emitting surface, and to methods of manufacturing such devices.
2. Description of the Related Art
Semiconductor light-emitting devices, in which a part of light emitted from a semiconductor light-emitting chip is converted into light having a different light-emitting wavelength by a wavelength converting resin including a phosphor and in which a mixture light comprises the light having the different light-emitting wavelength mixed with the light emitted directly from the semiconductor light-emitting chip is emitted, have been widely known as a light source for various lighting units. As conventional semiconductor light-emitting devices including a wavelength converting material, a first conventional semiconductor light-emitting device is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2004-343149).
FIG. 6 is an enlarged cross-sectional view showing the first conventional semiconductor light-emitting device, which is disclosed in Patent Document No. 1. The first conventional semiconductor light-emitting device 80 includes: a base board 85 having a bonding pad 86 formed in a rectangular tabular shape; a semiconductor light-emitting chip 81 having a top electrode mounted on the base board 85, and the top electrode being electrically connected to the bonding pad 86 via a bonding wire 87; a transparent encapsulating resin 82 having a top surface disposed on the base board 85 so as to cover the semiconductor light-emitting chip 81 along with the bonding wire 87; and a wavelength converting material 83 including a phosphor, which wavelength-converts a part of light emitted from the semiconductor light-emitting chip 81 into light having a different light-emitting wavelength from a light-emitting wavelength of the light emitted from the semiconductor light-emitting chip 81.
The conventional semiconductor light-emitting device 80 may emit a relatively uniform mixture light, which comprises the light having the different light-emitting wavelength mixed with the light emitted directly from the semiconductor light-emitting chip 81, from a top surface of the wavelength converting material 83. However, the semiconductor light-emitting device 80 may emit light including a comparative large amount of the light wavelength-converted by the phosphor from a side surface of the wavelength converting material 83 because the wavelength-converted light has a long path length in wavelength converting material 83
In addition, the semiconductor light-emitting device 80 may emit light including a large amount of the direct light emitted from the semiconductor light-emitting chip 81 from a side surface of the transparent encapsulating resin 82, because the direct light may not necessarily pass through the wavelength converting material 83. Accordingly, the first conventional light-emitting device 80 may be easy to vary a color tone of the mixture light depending on a light-emitting direction thereof.
FIG. 7a is an enlarged top view showing a second conventional semiconductor light-emitting device, which is disclosed in Patent Document No. 2 (Japanese Patent Application Laid Open JP2009-94199), and FIG. 7b is an enlarged cross-sectional view showing the second conventional semiconductor light-emitting device taken along line B-B′ shown in FIG. 7a. The second conventional semiconductor light-emitting device 70 includes: a base board 71 formed in a rectangular tabular shape; a semiconductor light-emitting chip 73 mounted on the base board 71 and emitting blue light during operation; and a wavelength converting material 74 having a side surface 76, an inclined surface 77 and a top surface 78, and including a yellow phosphor 72, which wavelength-converts a part of the blue light into yellow light, and the wavelength converting material 74 disposed on the base board 71 so as to cover the semiconductor light-emitting chip 73 therewith.
The wavelength converting material 74 may be formed in a substantially square frustum such that a square frustum having a bottom surface is exactly located on a square column having a top surface, which is the same square shape as the bottom surface of the square frustum. Therefore, because each of light path lengths emitted from the semiconductor light-emitting chips 73 toward the top surface 78, the inclined surface 77 and the side surface 76 may be approximately same, a color variability of a mixture light emitted from a light-emitting surface of the second conventional semiconductor light-emitting device 70, which is composed of the top surface 78, the inclined surface 77 and the side surface 76, may reduce.
However, each of structures such as the above-described first and second conventional light-emitting devices 80 and 70 are configured to cover the semiconductor light-emitting chips 81 and the semiconductor light-emitting chip 73 with the transparent encapsulating resin 82 and the wavelength converting material 74 along with the base boards 85 and 71, respectively. Consequently, each of parts of lights, which get to the side surface of the transparent encapsulating resin 82 and the side surface 76 and the inclined surface 77 of the wavelength converting material 74, may returns toward the base boards 85 and 71 by reflecting on the side surfaces and the like described above, and may be reflected by the base boards 85 and 71, respectively. Therefore, the above-described structures may be difficult to maintain a high contrast between a light-emitting surface and a non-light-emitting surface in top views of the semiconductor light-emitting devices, although each direction of the top views may be a light-emitting direction of the devices.
When the semiconductor light-emitting devices having such structures are used as a light source for a lighting unit such as a vehicle headlight, which controls light emitted from the semiconductor light-emitting devices using a reflector and/or a projector lens, a light-emitting device having a small light-emitting surface in addition to the high contrast may be desired to efficiently control light emitted from the semiconductor light-emitting device with a small optical structure. Therefore, the semiconductor light-emitting devices disclosed in Patent Documents No. 1 and No. 2 may not be a match for the above-described usage.
A conventional semiconductor light-emitting device having a small light-emitting surface and a high contrast can be used as a light source for a vehicle headlight using a projector lens and is disclosed in Patent Document No. 3 (Japanese Patent Application Laid Open JP2009-135136). FIG. 8a is an enlarged cross-sectional view showing a third conventional semiconductor light-emitting device disclosed in Patent Document No. 3, and FIG. 8b is a graph showing an exemplary high contrast measured from an upward direction of the third conventional device shown in FIG. 8a. 
The third conventional semiconductor light-emitting device 90 includes: a semiconductor chip substrate 91 configured not to transmit light; a semiconductor epitaxial layer 92 formed on the chip substrate 91; a wavelength converting layer 94 including a transparent resin 96 and a phosphor 95, disposed on the semiconductor chip substrate 91 so as to cover the semiconductor epitaxial layer 92 therewith, and being formed in a substantially dome shape; and a mounting board 97 mounting the chip substrate 91, which mounts the semiconductor epitaxial layer 92 thereon along with the wavelength converting layer 94.
According to such a structure, the third conventional semiconductor light-emitting device 90 may not emit light from a side surface of the semiconductor chip substrate 91, and also may not reflect light by the mounting board 97 because the semiconductor chip substrate 91 may not transmit light. Accordingly, as shown in FIG. 8b, the third conventional semiconductor light-emitting device 90 can perform a high contrast between a light-emitting surface and a non-light-emitting surface such that a light-emitting intensity thereof sharply rises from the non-light-emitting surface to the light-emitting surface.
In addition, because the above-described structure is forming the wavelength converting layer 94 in the substantially dome shape on the minute semiconductor chip substrate 91 while the wavelength converting layer 94 encapsulates the finer semiconductor epitaxial layer 92 on the minute semiconductor chip substrate 91, the third conventional semiconductor light-emitting device 90 may be used as a point light source as compared with the structure such as the first and the second conventional devices 80 and 70, in which each of the whole semiconductor light-emitting chips 81 and 73 is encapsulated with the transparent resin 82 and the wavelength converting material 74, respectively.
Moreover, because the wavelength converting layer 94 may be formed in the substantially dome shape, thicknesses of the wavelength converting layer 94 in light-emitting directions from the semiconductor epitaxial layer 92 toward a light-emitting surface may be comparatively uniform. Therefore, the third conventional semiconductor light-emitting device 90 may reduce a chromatic variability in the light-emitting directions from the semiconductor epitaxial layer 92 toward the light-emitting surface.
However, technically a path length of light emitted from a middle portion of the semiconductor epitaxial layer 92 in a directly up direction of the semiconductor light-emitting device 90 may be longer than that of light emitted from a peripheral portion of the semiconductor epitaxial layer 92 because the wavelength converting layer 94 is formed in the substantially dome shape. Accordingly, the light emitted from the middle portion of the semiconductor epitaxial layer 92 in the directly up direction of the light-emitting device 90 may include a larger amount of light wavelength-converted by the wavelength converting layer 94 as compared with the light emitted form the peripheral portion of the semiconductor epitaxial layer 92.
When the structure such as the third conventional semiconductor light-emitting device 90 is used as light source for general lighting units such as a general lighting, an indicator and the like, such a slight color variability may not cause any interferences to the general lighting units. However, when the structure is used as a light source for a lighting unit such as a vehicle headlight, which enlarges light emitted from the semiconductor light-emitting device using a reflector and/or a projector lens and projects the light in the distance, the slight color variability may not necessarily neglected in order to provide various expensive-looking lighting units using the reflector and/or the projector lens.
Such the structure may reduce the sight color variability by controlling a thickness and a density of the wavelength converting material 94 near the peripheral portion of the semiconductor epitaxial layer 92. However, because a size of the semiconductor chip substrate 91 may generally be approximately several hundred micro square meters to one square millimeter, it may be difficult for a molding method, which is usually used for a low coast, to control the thickness and the like of the wavelength converting material 94.
The above-referenced Patent Documents are listed below, and are hereby incorporated with their English abstracts in their entireties.    1. Patent Document No. 1: Japanese Patent Application Laid Open JP2004-343149    2. Patent Document No. 2: Japanese Patent Application Laid Open JP2009-94199    3. Patent Document No. 3: Japanese Patent Application Laid Open JP2009-135136
The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, embodiments of the disclosed subject matter can include semiconductor light-emitting devices that can emit a mixture light having a high uniform color tone from a small light-emitting surface, in which the mixture light can be emitted with a small color variability along an optical axis thereof, and also can be emitted with a small color variability even in a different light-emitting direction from the optical axis. The embodiments of the disclosed subject matter can also include associated manufacturing methods that do not cause and/or are designed to prevent some of the above-described problems, concerns, and characteristics related to a wavelength converting layer.